The fine and finest crushing of brittle material to be comminuted in the gap between two rolls which are pressed against one another at high pressure is known for example from German Patent Specification No. B-2708053. In that publication the material to be comminuted undergoes material bed crushing in the roll gap. If the material for comminution is delivered with a grain size which is greater than the width of the roll gap, on passing through the roll gap the material first of all undergoes individual grain crushing and immediately thereafter material bed crushing.
In the past the material to be comminuted was generally delivered to the roll gap purely by the effect of gravity via a delivery shaft in which such material reaches a certain filling level.
However, it has now been shown that certain materials tend to slip on the rolls or are not drawn satisfactorily into the roll gap. Such difficulties occur for example in the case of coal with high moisture content.
A further problem lies in ensuring that the crushing effect and with it the nature of the product remains constant within narrow limits over a wide range of variation of the throughput.
The object of the invention, therefore, is to provide apparatus and methods of the type referred to for crushing of materials of all types, and in particular also with material which tends to slip on the rolls, whereby satisfactory drawing in of the material into the roll gap is ensured and a constant crushing effect (product granulation) is achieved irrespective of the nature of the product with a throughput which varies over a wide range.